In recent years, a solar energy generation system is prevailing as a way of generating electricity utilizing clean energy. Solar cell modules are generally composed of three layers of a glass, a cell for a solar cell (a semiconductor cell) and a back sheet.
The back sheet protects the cell so as to avoid the degradation of the cell, thereby serving to maintain its generating efficiency. Such a back sheet is requested to have excellent mechanical property, heat resistance, and weatherability. JP-A 2002-26354 and JP-A-2003-60218, for example, disclose a protective film for the back side of a solar cell using a polyethylene terephthalate film.
Solar cells are requested to have high barrier property since those are put in outdoors for long years. As a result, it is investigated to use a laminate film in which an organic layer and an inorganic layer are laminated on a substrate film. In order to produce such a laminate film at low cost, a roll to roll processing which can produce a large-area film at high speed is chosen. When the laminate film is produced by the roll to roll processing, its important factor is its friction and slidability between a substrate film and a pass roller in transferring the substrate film at high speed, or its friction and slidability of laminated layers. That is, the film must be optimized in slidability. When the laminate film is poor in slidability, wrinkle often occurs in transferring or taking-up the film, and therefore, the slidability is highly demanded.
JP-A-2000-85067 discloses that the film satisfying a particular Ra is excellent in handability such as stickiness and the like and in hydrothermal resistance of the vapor-deposited layer. On the other hand, JP-A-6-340046 discloses that a film excellent in adhesiveness and slidability is obtained by adjusting prominence of the film.